In an automobile, various kinds of information for performing the control thereof are required; therefore, it has been proposed to provide a sensor device to a hub unit including a body-side raceway member to be fixed to the vehicle body side, a wheel-side raceway member to which a wheel is to be mounted, and two rows of rolling elements disposed between the both members. For example, Patent Document 1 (Japanese Unexamined Patent Publication No. 3-209016) discloses a hub unit with a sensor in which an annular support member is mounted on an inner end face of a body-side raceway member, and a strain sensor is mounted to the annular support member.
In recent years, control means of an automobile include, in addition to an ABS (Antilock Braking System) control, a driving force control for not causing drive wheels to spin when starting or accelerating, and a braking force control for suppressing skidding when cornering. In order to control the automobile more accurately, it is important to detect data which can be used effectively for these controls. In view of the above circumstance, the present inventors set an object to improve the control of vehicles by accurately measuring grounding loads placed on tires (wheels).
However, since the hub unit with a sensor of Patent Document 1 is adapted to measure the strain of the annular support member, there was a problem that when the tire grounding load was obtained from the strain, an error became large, so that the tire grounding load could not be obtained with high accuracy from the measurement values of the strain sensor. In view of this problem, the present inventors proposed to obtain the tire grounding load with high accuracy by using magnetostrictive sensors (Patent Document 2=Japanese Patent Application No. 2002-142417).
According to the hub unit with a sensor of Patent Document 2, if a location to which a magnetostrictive sensor is mounted is appropriate, expected effects are obtained, but if a location to which a magnetostrictive sensor is mounted is inappropriate, the inverse magnetostrictive effect to be detected is smaller. As a result, there has been a case that an error in the tire grounding load to be obtained is large. Further, although it is desired to extract only left-and-right directional components among tire grounding loads as data preferable for vehicle control, there has been a problem that if a location to which the magnetostrictive sensor is mounted is inappropriate, the left-and-right directional tire grounding load cannot be obtained with high accuracy.
An object of the present invention is to provide a hub unit with sensors capable of making mounting positions of the sensors appropriate when mounting sensors (including not only magnetostrictive sensors but also displacement sensors) by specifying a location where the inverse magnetostrictive effect or the displacement amount becomes larger in the hub unit to thereby enable to determine tire grounding loads with high accuracy by using the sensors, and capable of determining by extracting not only an up-and-down directional tire grounding load, but only a left-and-right directional tire grounding load, or determining by extracting an up-and-down directional tire grounding load and a left-and-right directional tire grounding load, respectively.